5860
Macromolecules 1999, 32, 5860-5871
Crystal Structure of Ethylene-Vinyl Alcohol Copolymers Masahide Takahashi,*,† Kohji Tashiro,*,‡ and Shigetoshi Amiya† Analytical Research Center, Kuraray Co., Ltd., Kurashiki, Okayama 710-8691, Japan, and Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Received April 8, 1999; Revised Manuscript Received June 10, 1999
ABSTRACT: Crystal structures of ethylene-vinyl alcohol copolymers (EVOH) with various vinyl alcohol (VA) compositions have been determined on the basis of the X-ray diffraction data measured for the uniaxially and doubly oriented sample specimens. The unit cells of EVOH with a VA content higher than 27 mol % are monoclinic of the space group P1121/m, in which the two planar-zigzag chains are statistically packed in a mode similar to that of poly(vinyl alcohol) (PVOH). With a decreasing VA content from 27 to 14 mol %, the crystal system approaches the hexagonol type. The unit cells of EVOH with a VA content below 14 mol % are orthorhombic of the space group Pnam, similar to the packing mode of orthorhombic polyethylene (PE). The crystal structure of EVOH with the VA content in the range of 14-27 mol % is the pseudohexagonal type. In this way the transformation of the unit cell structure between the PVOH type (>27 mol %) and PE type (
